Road bike: These are the sports cars of the biking world. Yes, geometry among the sub-categories vary along with materials and components. However, when all is said and done we are still talking about racing for speed.
Mountain bike: Whether no suspension, hard tail, or fully suspended it's still a mountain bike. If you take the beefier frame and add skinny road tires you have a commuter bike. Similarly, if you add stronger wider wheels on a road bike you end up with a cross bike.
BMX: Think X and gravity games. Dirt track racers or half pipe riding freestylers all ride that same basic frame and components with event specific variations.
Now consider how ludicrous city auto travel would be if the choices were similarly limited.
"My sports car is for weekend racing but I'll put a trailer on it for the annual camping trip."
Look what the guys at autospies.com found. Crazy Right?
How about, "Honey did you charge up the Hummer last night? I need to pick up groceries and drop of my dry cleaning."
There had to be a better use of brain power back in '09
The car market has sedans, wagons, SUVs, sports cars and so on. Make room for purpose built cargo bikes in the FMZ (five mile zone around your home). Leave your road bike for the century ride. With a cargo bike you simply get on, go, and get as much stuff as you need depending on the model. I still haven't purchased enough groceries to overload a cargo bike.
Xtracycle Radish Rex Hazard
Stephen Mosca of Go-one LLC said it best in this faircompanies.com video on velomobiles. "Think of your garage as a transportation tool box." Use the right tool for the job. Enjoy your city at a pace you can actually taking your surroundings and get as much or as little of a workout in as you like. Electric assist is an option if necessary.
Would you prefer a function specific bike or general use with cargo accessories?